1. Field of the Invention
This invention relates to powerline communication networks, and more particularly to a method and apparatus for medium access control in powerline communication network systems.
2. Description of Related Art
The past few years have brought about tremendous changes in the modem home, and especially, in appliances and other equipment designed for home use. For example, advances in personal computing technologies have produced faster, more complex, more powerful, more user-friendly, and less expensive personal computers (PCs) than previous models. Consequently, PCs have proliferated and now find use in a record number of homes. Indeed, the number of multiple-PC homes (households with one or more PCs) is also growing rapidly. Over the next few years, the number of multiple-PC homes is expected to grow at a double-digit rate while the growth from single-PC homes is expected to remain flat. At the same time, the popularity and pervasiveness of the well-known Internet has produced a need for faster and less expensive home-based access.
As is well known, usage of the Internet has exploded during the past few years. More and more often the Internet is the preferred medium for information exchange, correspondence, research, entertainment, and a variety of other communication needs. Not surprisingly, home-based based Internet usage has increased rapidly in recent years. A larger number of homes require access to the Internet than ever before. The increase in home Internet usage has produced demands for higher access speeds and increased Internet availability. To meet these needs, advances have been made in cable modem, digital subscriber loop (DSL), broadband wireless, powerline local loop, and satellite technologies. All of these technologies (and others) are presently being used to facilitate home-based Internet access. Due to these technological advances and to the ever-increasing popularity of the Internet, predictions are that home-based Internet access will continue to explode during the next decade. For example, market projections for cable modem and DSL subscriptions alone show an imbedded base of approximately 35 million connected users by the year 2003.
In additions to recent technological advances in the personal computing and Internet access industries, advances have also been made with respect to appliances and other equipment intended for home use. For example, because an increasing number of people work from home, home office equipment (including telecommunication equipment) has become increasingly complex and sophisticated. Products have been developed to meet the needs of the so-called SOHO (“small office, home office”) consumer. While these SOHO products tend to be less expensive than their corporate office product counterparts, they do not lack in terms of sophistication or computing/communication power. In addition to the increasing complexity of SOHO products, home appliances have also become increasingly complex and sophisticated. These so-called “smart” appliances often use imbedded microprocessors to control their functions. Exemplary smart appliances include microwaves, refrigerators, dishwashers, washing machines, dryers, ovens, etc. Similar advances have been made in home entertainment systems and equipment such as televisions (including set-top boxes), telephones, videocassette recorders (VCRs), stereos, etc. Most of these systems and devices include sophisticated control circuitry (typically implemented using microprocessors) for programming and controlling their functions. Finally, many other home use systems such as alarm systems, irrigation systems, etc., have been developed with sophisticated control sub-components.
The advances described above in home appliance and equipment technologies have produced a need for similar advancements in home communication networking technology. As home appliances and entertainment products become increasingly more complex and sophisticated, the need has arisen for facilitating the interconnection and networking of the home appliances and other products used in the home. Also, a need for distribution of entertainment media such as PC applications, audio streaming and voice telephony exists. One proposed home networking solution is commonly referred to as “Powerline Networking”. Powerline networking refers to the concept of using existing residential AC power lines as a means for networking all of the appliance and products used in the home. Although the existing AC power lines were originally intended for supplying AC power only, the Powerline Networking approach anticipates also using the power lines for communication networking purposes. One such proposed powerline networking approach is shown in the block diagram of FIG. 1.
As shown in FIG. 1, the powerline 100 comprises a plurality of power line outlets 102 electrically coupled to one another via a plurality of power lines 104. networkAs shown in FIG. 1, a number of devices and appliances are coupled to the powerline network via interconnection with the plurality of outlets 102. For example, as shown in FIG. 1, a personal computer 106, laptop computer, 108, telephone 110, facsimile machine 112, and printer 114 are networked together via electrical connection with the power lines 104 through their respective and associated power outlets 102. In addition, “smart” appliances such as a refrigerator 115, washer dryer 116, microwave 118, and oven 120 are also networked together using the proposed powerline network 100. A smart television 122 is networked via electrical connection with its respective power outlet 102. Finally, as shown in FIG. 1, the powerline network can access an Internet Access Network 124 via connection through a modem 126 or other Internet access device.
With multiple power outlets 102 in almost every room of the modern home, the plurality of power lines 104 potentially comprise the most pervasive in-home communication network in the world. The powerline network system is available anywhere power lines exist (and therefore, for all intents and purposes, it has worldwide availability). In addition, networking of home appliances and products is potentially very simple using powerline networking systems. Due to the potential ease of connectivity and installation, the powerline networking approach will likely be very attractive to the average consumer. However, powerline networking systems presents a number of difficult technical challenges. In order for powerline networking systems to gain acceptance these challenges will need to be overcome.
To appreciate the technical challenges presented by powerline networking systems, it is helpful to first review some of the electrical characteristics unique to home powerline networks. As is well known, home power lines were not originally designed for communicating data signals. The physical topology of the home power line wiring, the physical properties of the electrical cabling used to implement the power lines, the types of appliances typically connected to the power lines, and the behavioral characteristics of the current that travels on the power lines all combine to create technical obstacles to using power lines as a home communication network.
The power line wiring used within a house is typically electrically analogous to a network of transmission lines connected together in a large tree-like configuration. The power line wiring has differing terminating impedances at the end of each stub of the network. As a consequence, the transfer function of the power line transmission channel has substantial variations in gain and phase across the frequency band. Further, the transfer function between a first pair of power outlets is very likely to differ from that between a second pair of power outlets. The transmission channel tends to be fairly constant over time. Changes in the channel typically occur only when electrical devices are plugged into or removed from the power line (or occasionally when the devices are powered on/off). When used for networking devices in a powerline communications network, the frequencies used for communication typically are well above the 60-cycle AC power line frequency. Therefore, the desired communication signal spectrum is easily separated from the real power-bearing signal in a receiver connected to the powerline network.
Another important consideration in the power line environment is noise and interference. Many electrical devices create large amounts of noise on the power line. The powerline networking system must be capable of tolerating the noise and interference present on home power lines. Some of the home power line interference is frequency selective. Frequency selective interference causes interference only at specific frequencies (i.e., only signals operating at specific frequencies are interfered with, all other signals experience no interference). However, in addition, some home power line interference is impulsive by nature. Although impulsive interference spans a broad range of frequencies, it occurs only in short time bursts. Some home power line interference is a hybrid of these two (frequency selective and impulsive). In addition to the different types of interference present on the home power lines, noise is neither uniform nor symmetrical across the power lines. For example, noise proximate a first device may cause the first device to be unable to receive data from a second, more distant device; however, the second device may be able to receive data from the first. The second device may be able to receive information from the first because the noise at the receiver of the second device is attenuated as much as is the desired signal in this case. However, because the noise at the receiver of the first device is not as attenuated as is the desired signal (because the noise source is much closer to the first device than the second), the first device will be unable to receive information from the second.
Another consideration unique to powerline networking systems is that home power line wiring typically does not stop at the exterior wall of a house. Circuit breaker panels and electric meters (typically located outside the home) pass frequencies used for home networking. In typical residential areas, a local power transformer is used to regulate voltage for a fairly small number of homes (typically between 5 and 10 homes). These homes all experience relatively small amounts of attenuation between each other. The signal frequencies of interest to powerline networking systems do not tend to pass through the transformer. Due to these electrical characteristics, signals generated in a first home network can often be received in a second home network, and vice versa. In addition, unlike internal dedicated Ethernet or other data networks, power lines are accessible from power outlets outside of the home. This raises obvious security concerns because users typically do not want to share information with unauthorized users including their neighbors.
Signals that travel outside of the house tend to encounter greater attenuation than those that originate in the same house, and thus the percentage of outlets having house-to-house connectivity is much lower than the percentage for same house connectivity. The fact that transmissions at some outlets may not be receivable at other outlets is a significant difference between powerline networking systems and a wired LAN-type communication network such as the well-known Ethernet.
Despite these and other technical concerns, powerline communication network systems are presently being developed and proposed. For example, the HomePlug™ Powerline Alliance has proposed one such powerline communication network. The HomePlug™ Powerline Alliance is a non-profit industry association of high technology companies. The association was created to foster an open specification for home powerline networking products and services. Once an open specification is adopted, the association contemplates encouraging global acceptance of solutions and products that employ it.
A very important aspect of any home powerline networking system specification is the definition of a Medium Access Control (“MAC”) communication protocol. The MAC protocol should be designed to allow devices to share the powerline network in a fair manner that provides performance in terms of delivered throughput, latency, and acceptable errors. The MAC should facilitate powerline networking system performance suitable for a number of applications including file transfer, voice, networked gaming, and streaming audio/video. The MAC protocol should be designed specifically to address the technical challenges posed by powerline networking systems. For example, the MAC communication protocol for powerline networking systems should ease compatibility of upgraded devices and protocols. That is, the MAC should ease the efforts associated with installing and operating upgraded (i.e., newer version) powerline networking system protocols and devices. Heretofore, it has been very difficult (if not impossible) to operate newer version devices on powerline ing systems operating older version devices. Therefore, there is a need for a MAC protocol that eases the task of upgrading powerline networking system protocols and devices.
In addition, the prior art attempts do not provide a mechanism for establishing “circuit-like” connections wherein devices are connected together via a “virtual circuit.” Most prior art network systems use a “contention-based” access approach. In this mode of access, when a device has data to send, it first determines whether a channel is being used by another device, and if it is not, the device begins data transmission. Other devices refrain from transmitting on the channel until the first device terminates its transmission. When more than one device requires transmission, a “collision” occurs and the devices re-transmit their data because procedures defined in the prior art MAC protocol require data re-transmission. As traffic on the channel increases, so too do the number of collisions, resulting in data transmission delays. The exact period of the delay is not fixed, but varies depending upon traffic characteristics. These delays may be acceptable for some applications (such as file transfers), but not others (such as streaming audio/video). The prior art solutions include use of priority schemes whereby “real-time” applications are assigned higher priorities than non-real-time applications. Disadvantageously, this approach is not ideal when there are multiple high priority users as they must still contend with one another and thus still encounter probabilistic delays. This prior art approach also disadvantageously allows a low priority device to monopolize use of a channel (once it gains use of the channel) even when there are higher priority devices waiting to use the channel.
Therefore, there is a need for a MAC protocol that overcomes the disadvantages associated with the prior art solutions. A need exists for a MAC communication protocol that permits the reservation of transmission time between devices requiring “circuit-like” connections, and especially in environments wherein no central controller is used (such as those contemplated for use in powerline networking systems). A need exists for a MAC that facilitates the establishment of “virtual circuits” between devices in a powerline networking system. The MAC should tightly control transmission delays in a powerline networking system.
Further, any MAC designed for use in powerline networking systems should provide for the management and distribution of encryption keys, even in network environments having no central controller. For example, the powerline networking systems currently being proposed and developed (such as the powerline network 100 of FIG. 1) do not contemplate use of central network controllers. One important aspect of MAC protocols designed for use in powerline networking systems is the control and distribution of encryption keys, especially in a controller-less network environment. In devices having user input/output (I/O) capabilities, encryption keys (or passwords that can be converted into encryption keys using a “hashing algorithm” or similar means) can be manually entered from the device. However, many devices may not have user I/O capability therefore making manual key entry impossible. Therefore, a need exists for a MAC communication protocol for powerline networking systems that facilitates the control and distribution of encryption keys, including the management of encryption keys for devices not having user I/O capability.
Finally, any MAC designed for use in powerline networking systems should provide for the unique assignment of logical network identifiers (“LNI”). Although all of the devices in a powerline networking system share the same physical medium (i.e., the home power lines such as the power lines 104 of FIG. 1), it is desirable to be able to separate the devices into logical networks (“LN”) wherein only those devices belonging to the same logical network are allowed to share data. Using encryption schemes, data can be shared between devices that are members of a given LN, but is protected from devices that are not members of the given LN. It is very convenient and efficient to permit a device in an LN to determine which LN it belongs to. The device can use this information to determine whether it should attempt to receive a given data packet. For example, this can be accomplished by including the LNI in each data packet transmission. Alternatively, this can be accomplished by including a management message in which the transmitting device indicates its LNI. Under ideal conditions, each LN sharing the same physical medium should have a unique identifier. In powerline networking systems wherein no central controller exists, there is no convenient means for ensuring that LNIs are not accidentally re-used. For example, it is not likely that home owners would feel comfortable asking their neighbors which LNI they have selected for their LN. Therefore, a need exists for a MAC protocol for a powerline networking system that facilitates the assignment of unique Logical Network Identifiers that are not accidentally re-used by the system.
The present invention provides such a method and apparatus for Medium Access Control in powerline communication network systems.